The invention relates to rotary electrostatic spray applicators known as bell cup applicators for applying powder coatings to substrates. Such bell cup powder applicators are affixed to turbine housings through which are fed the powder to be sprayed in the form of an air-powder mixture under pressure. Electrostatic bell cup powder spray applicators are used to spray coat automotive vehicles, and various such devices are known. For example, U.S. Pat. No. 5,353,995 discloses a rotating ionizer head for the electrostatic application of an air-powder mixture, for coating objects with powder paint which is subsequently fused by heat. The ionizer head is rotated by a turbine and includes a deflector incorporating a charging electrode.
In such applications, the coating material is generally applied as a fine powder spray which is subsequently baked in a vehicle paint oven to form a durable coating thereon. As a substrate passes the rotating coating bell cup applicator assembly, electrically charged powder particles are discharged in a mist form. The ionized powder particles are attracted to the electrically charged (grounded) substrate to provide an evenly distributed coating on the substrate.
These spray applicators have a turbine body housing connected to a pneumatic line and a powder supply and delivery line. The turbine body is housed within the housing and motivates the air/powder mixture therethrough to the bell cup applicator assembly mounted at the forward end thereof. The powder passing axially through the turbine housing is ejected through the mount at the center of the rotating bell cup, which is maintained at a high voltage, and impinges on the rotating deflector thereof, at which it is redirected radially outwardly therefrom, forming the aforesaid powder mist used in coating various substrates.
The bell cup is generally shaped as a truncated frusto-conical body member, with its smaller diameter end oriented toward the turbine air/powder supply, and its larger diameter end flaring outwardly to its periphery. Spaced apart from the bell cup, and forming a uniform gap at the periphery thereof, is a deflector, which has a convex surface and which, in cooperative alignment with the bell cup, forms an annular, tapering passageway extending from the central, axial air/powder delivery passageway and tapering to the outer, peripheral uniform gap, from which the powder is ejected to coat a substrate passing thereby.
Powder that is forced under pressure axially through the bell cup assembly housing impinges upon the deflector as aforesaid, which is rotating at a high rate, and this powder is re-directed radially outwardly by vanes or paddles which are affixed within the passageway between the bell cup and deflector, and which drive the powder radially outwardly through the gap, forming essentially a frusto-conical ring of air and powder directed toward the substrate to be coated.
Other, electrostatic powder spraying devices having rotating, ionizing heads are known, e.g., in U.S. Pat. No. 4,114,564. In such devices, ionically charged powder particles flow from the spray assembly to the object to be coated, such as a vehicle, maintained at ground potential. The powder coating is subsequently baked thereon to form a uniform, durable coating on the substrate.
A rotatable powder bell cup electrostatic spray assembly is provided. This assembly is removably and coaxially attachable to rotational drive means which are attached to a non-rotating housing and feed nozzle through which a mixture of air and powder may be fed into the assembly. More specifically, this assembly includes a generally bell shaped body member removably and threadably connected concentrically to a first deflector member having connecting means removably and threadably insertable into the body member. The body member and first deflector member are cooperatively configured to form, when connected together, a tapered annular passageway therebetween extending from the rotational center thereof and tapering outwardly therefrom to the respective outer peripheries of the body member and first deflector member. At their outer peripheries these members form a uniform gap having a precision circumferential spacing therearound. The electrostatic spray assembly includes, within this passageway, a plurality of pillar-like, streamlined deflecting vanes extending generally perpendicularly from the first deflector member through this passageway, each vane containing at least one electrical connector therein which extends therethrough and which electrically connects an ionizing source in the housing to a conducting faceplate affixed to the external face of the first deflector, remote from the passageway. The faceplate has an emitting electrode extending externally from its axial center thereof. The body member and the first deflector member and the deflecting vanes are all constructed of electrically insulative material, preferably a non-stick plastic material, and polytetrafluoroethylene, e.g., Teflon(copyright), is preferred.
In a preferred embodiment, the plurality of deflecting vanes and the first deflector member are integrally formed as a unitary construct. In addition, the deflecting vanes are streamlined in cross-sectional shape with respect to flow of powder particles thereover, and these streamlined deflecting vanes are preferably configured in the shape of teardrops having their respective forward edges blunt and rounded and their respective trailing edges tapered.
In the entire assembly, all surfaces adjacent to which the air/powder mixture flows are streamlined, that is, rounded, and contain no sharp corners. The body member and the first deflector member, at their respective outer peripheries at which these members form the discharging gap, have radiused edges.
The assembly has a faceplate electrically connected to the ionizing source in the housing by the electrical connectors passing through openings extending through the vanes, one connector within each vane, thereby isolating high voltage from all internal surfaces within this assembly over which the air/powder mixture flows. Each electrical conductor may be a conducting spring, constructed of a noncorrosive metal such as stainless steel.
The aforesaid connecting means may include at least one adjustable spacer which determines the insertion distance available to the first deflector member upon insertion into the body member. This spacer provides calibrated adjustability of the circumferential uniform gap spacing about the periphery of the assembly. This spacer may be a shim having a thickness in the range of 0.10 mm. to 1.00 mm., or other suitable thickness.